In my above-mentioned co-pending application entitled "Diamagnetic Colloids Containing Superconducting Particles", I have described my invention of a new family of colloids which I have formed by mixing in a liquid a dispersion of particles that are superconducting. I have shown in the same cited application that such particles can be kept in suspension indefinitely in the presence of a magnetic field, and thus the suspension behaves as a perfect colloid as long as that magnetic field is present. I have also shown that this surprising behavior is probably due to the Meissner effect on each particle and the resulting mutual magnetic field expulsion. I have termed these unique colloids "Diamagnetic Colloids", and this term is used herein.
Until recently, it was believed that superconductivity above 23.degree. K. is not possible. This belief was rooted in the theoretical work now named the BCS (Bardeen, Cooper and Schrieffer) theory which predicted such an upper limit. As a result no research in the field of emulsions and suspension of superconducting particles in liquids can be cited. Under 23.degree. K., all matter except helium and hydrogen assumes the solid state, thus limiting the application of such colloids.
The highest temperature at which superconductivity occurs in a superconductor (in the absence of any external magnetic fields) is termed the critical temperature of that superconductor and this term will be used herein.
In the early 1970's a number of theoretical proposals were presented, suggesting that the critical temperature for superconductivity could be increased. (V. L. Ginzburg, Usp. Fiz. Nauk. 101, 185 (1970)) (D. Allender, J. Bray, J. Bardeen, Phys. Rev. B8, 4433 (1973)), but the lack of any discoveries of superconductivity above 23.degree. K., solidified the belief that indeed this critical temperature cannot be exceeded. A significant experimental breakthrough in high temperature superconductivity (critical temperatures in excess of 23.degree. K.) was provided in November 1986 by Bednorz and Muller when they published a tentative disclosure of high temperature superconductivity (Georg Bednorz and Alex Muller, Z. Phys. B64, 189 (1986)), which was rapidly confirmed by others; for instance, a report, cites a critical temperature above 30.degree. K. for La.sub.(2-x) Ba.sub.(x) CuO.sub.(4-y), (H. Takagi, S. Uchida, K. Kitazawa, S. Tanaka, Jpn. J. Appl. Phys. 26, L123 (1987)).
Confirmation of a critical temperature of 93.degree. K. was reported by Chu for yttrium-barium-copper oxide ceramic (M. K. WU, J. R. Ashburn, C. J. Tang, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang, and C. W. Chu, Phys. Rev. Lett. 58, 2 Mar., 1987, p. 908.) This material was dubbed the 123 compound and served as a model for advanced research in the field.
During 1987 and 1988, a number of families of high temperature superconductors where discovered with confirmed critical temperatures all the way to 162.degree. K. These materials are usually ceramics containing copper (some of which must be in the trivalent state), an alkaline metal (Ca, Sr, or Ba) and a rare earth including Yttrium.
There are some scattered reports of superconductivity above 162.degree. K., for instance by R. G. Kulkarui who reports superconducting oxides having an approximate composition (CaO).sub.0.5 (ZnO).sub.0.5 Fe.sub.2 O.sub.4, and also Ogushi reporting superconductivity at room temperature in yet ill-defined niobium strontium lanthanum oxides. While these reports have yet to be confirmed independently by other researchers, it is reasonable to expect superconductors with critical temperatures at room temperature to become available in the near future.